A randomised trial of a common probiotic has shown that a daily dose substantially reduced episodes of diarrhoea and respiratory tract infections among children at day care centres. Researchers tested 336 healthy children ages 6 months to 3 years who were attending day care centres in Mexico City.

Half received a daily dose of Lactobacillus reuteri, a beneficial gut bacterium naturally present in many foods and in most people; the other half got an identical placebo.

The intervention lasted three months, and the children were followed for another three months without supplements. The study was published in Pediatrics and was supported by a grant from a manufacturer of probiotic supplements.

During the study, there were 69 episodes of diarrhoea in the placebo group and 42 in the supplement group. The placebo group had 204 respiratory tract infections, compared with 93 in those taking L. reuteri.